1. Field of the Invention
The present invention relates to a camera and, in particular, to an electronic still camera in which tele and wide lenses can be switched over to each other in actual use.
2. Description of the Related Art
Conventionally, there has been known an electronic still camera (which is disclosed in Japanese Patent Application No. 1-184019) in which a tele lens (T lens) and a wide lens (W lens) are mounted in a lens holder, the lens holder is rotatably supported on a lens support shaft, and the lens holder can be electrically rotated between a T lens using position and a W lens using position to thereby switch the T and W lenses to each other.
The above-mentioned lens support shaft is supported at the two ends thereof respectively by a lens mount base member and a mount cover member and, in the rear of the lens mount base member, a CCD reference plate with a CCD solid state image pick-up element (which is hereinafter referred to as CCD) on board is disposed in such a manner that the positions of the CCD reference plate can be adjusted at 3 points. Also, this camera is constructed such that a point of focus can be adjusted by inserting a parallel glass into the optical axis of a taking lens.
In general, in macro photographing, the depth of field becomes extremely shallow, thereby making focusing difficult. For this reason, conventionally, in the macro photographing, an iris is stopped down to thereby increase the depth of field so as to cover the focusing with the increased depth of field.
On the other hand, in an electronic still camera having an electronic shutter function, there is no need for variable stopping for adjustment of light quantity, because an electric charge accumulation time (that is, shutter speed), during which the light of an object to be photographed substantially enters the image pickup element, can be controlled electrically.
However, in the macro photographing, as described before, greater stopping-down is necessary than in an ordinary photographing so as to increase the depth of field. For this reason, a camera capable of macro photographing requires a variable diaphragm mechanism such as a rotary diaphragm adapted to vary stop values by rotating a disc with small and large stop apertures punched thereon, an iris diaphragm capable of varying successively aperture diameters, and the like.
In the above-mentioned conventional electronic still camera, the T and W lenses and the CCD are respectively arranged through the lens mount base member in such a manner that they have a constant positional relationship therebetween. Due to this, it is hard to adjust the position of the CCD. Also, as described before, the CCD reference plate must be constructed such that its positions can be adjusted at three points.
Also, the switching of the above-mentioned T and W lenses is performed by intermittently transmitting a rotational drive force from a motor through a triangular cam to the T and W lenses, while the advancing and retreating of the parallel glass is performed by transmitting a rotational drive force from the motor through a focus switching cam to the parallel glass while the T and W lenses are being stopped. In other words, the power transmission mechanism employed in the above conventional electronic still camera is complicated due to the fact that the switching of the T and W lenses and the advancing and retreating of the parallel glass plate are carried out by taking out the respective drive forces from a single motor by use of the triangular cam and the focus switching cam. Also, the parallel glass advancing and retreating method is not capable of successive focus adjustments and, when a multi-stage focus switching is performed, a plurality of parallel glass plates differing in thickness from one another must be prepared to switch these parallel glass plates to one another, which makes the parallel glass plates switching mechanism further complicated.
Further, in an electronic still camera having an electronic shutter function, mechanical elements are saved or simplified as much as possible to thereby reduce the size and weight of the camera as well as decrease the cost thereof. However, to add the above-mentioned macro photographing function to the camera, there is necessary a variable diaphragm mechanism such as a rotary stop diaphragm, an iris stop diaphragm and the like, resulting in the complicated structure and increase in costs.